1. Field of the Invention
The present invention relates to a molded product for a cushioning material (hereinafter referred to as xe2x80x9ccushioning molding productxe2x80x9d) composed mainly of a vegetable fiber, and to a process for production and recovery thereof.
2. Related Background Art
Molded products produced by binding and molding a vegetable fiber such as paper, cotton, straw, and strained lees with a suitable binder are widely used as a cushioning material for impact absorption.
In recent years, molded pulp products are coming to partially replace conventional foamed polystyrene-molded products used as a cushioning packing material for home electric appliances. The molded pulp products exhibit excellent properties of absorbing drop-impact and sound-wave, and readily moldable into sheets, pellets, or an arbitrary shape to fit to the shape of the package.
The molded pulp product is basically a paper product, and can readily be regenerated after use by fiber opening and sheet making. Besides, in the case where the regeneration is not suitable owing to the deterioration of the properties or other reasons, the molded pulp product can be burned or buried without releasing a toxic component to cause less adverse effect on the environment. Especially, the molded pulp product is advantageous from the standpoint of effective utilization of resources.
Various binders are used for producing the cushioning molded products. As the binders, polysaccharides are widely used in consideration of compatibility with the vegetable fiber and low environmental loading, the polysaccharides including starches, agars, mannan, alginic acid, and carboxymethylcellulose.
These polysaccharides, however, do not always have good processability because of insolubleness in solvents except water, lack of thermoplasticity, or other reasons. Use of a usual thermoplastic resin is disclosed (Japanese Patent Application Laid-Open No. 7-267276). However, the usual thermoplastic resin does not have sufficient compatibility with vegetable fibers. The polysaccharides are derived from a material other than the fiber.
The molded pulp product has disadvantages resulting from the production process. That is, molded pulp products are conventionally produced by a wet sheet-making process employing water, similarly as paper sheets. This process comprises drying of an aqueous slurry, requiring a long time and consuming much energy for the drying, and the productivity thereof is not high. In particular, this production process is disadvantageous for production of thick molded products of less directional dependence in cushioning properties for drop impact. Moreover, the large energy consumption generally causes emission of carbon dioxide gas, which is a cause of greenhouse effect. This is inconsistent with the intension of environmental protection of the molded pulp product itself.
The present invention intends to provide a cushioning molded product, which is excellent in strength, processability and recyclability, produced from a vegetable fiber as the main source material by maximally utilizing the feature of the vegetable fiber. The present invention intends to also provide the process for production of the cushioning molded product.
The present invention further intends to provide a process of producing the cushioning molded products from the vegetable fiber as the main source material with higher productivity and lower environmental loads.
The present invention provides a cushioning molded product produced by binding a vegetable fiber with a copolymer of a saccharide and an aliphatic dicarboxylic acid to conduct molding.
In a preferred embodiment, the vegetable fiber is paper or a fiber obtained by fiber opening of paper.
The saccharide is preferably a monosaccharide or an oligosaccharide with a polymerization degree of 6 or less. The saccharide may be partially substituted with an acetyl group. The number of substituting acetyl groups is preferably in the range of 0 to 2 per monosaccharide unit.
In a preferred embodiment of the present invention, the saccharide is a product of decomposition of a vegetable fiber, in particular, a product of decomposition of paper.
The aliphatic dicarboxylic acid preferably has an alkylene chain having 4 to 10 carbon atoms for the monosaccharide, and 6 to 10 carbon atoms for the oligosaccharide.
The vegetable fiber is contained at a content ranging preferably from 50 to 99 wt %, and the copolymer is contained at a content ranging preferably from 1 to 50 wt %.
The copolymer preferably contains a component with a weight-average molecular weight of 500 to 10000 at a content from 50 to 100 wt %.
The present invention also provides a process for producing the cushioning molded product from a copolymer of a saccharide and an aliphatic dicarboxylic acid, and a vegetable fiber, the process comprising:
(a) mixing or adhering the copolymer and the vegetable fiber, and
(b) molding a mixture resulting from step (a) into an intended shape by heating the mixture to bind the vegetable fiber with the copolymer.
In a preferred embodiment, the mixing step includes a step of mixing the copolymer and the vegetable fiber by use of a solvent containing water at a content ranging from 0 to 50%.
In another preferred embodiment, the production process comprises the steps of:
(a) adhering the copolymer with a pelletized vegetable fiber,
(b) filling a mixture of the pelletized vegetable fiber and the copolymer resulting from step (a) into a molding vessel, and
(c) molding the mixture into an intended shape by heating the mixture to bind the vegetable fiber with the copolymer.
In another preferred embodiment, the production process comprises the steps of:
(a) forming the vegetable fiber into an intended shape,
(b) adhering the copolymer with the vegetable fiber, and
(c) molding a mixture of the vegetable fiber and the copolymer resulting from step (b) by heating the mixture to bind the vegetable fiber with the copolymer.
In another preferred embodiment of the present invention, the mixing or adhering step includes a step of sprinkling powder of the copolymer onto a vegetable fiber impregnated with an organic solvent to allow the copolymer to adhere onto the fiber. Otherwise, the mixing or adhering step includes a step of spraying a solution of the copolymer in an organic solvent onto the vegetable fiber followed by drying to allow the copolymer to adhere onto the fiber.
In a preferred embodiment, the molding step includes the steps of filling the mixture of the copolymer and the vegetable fiber into a molding vessel, and heating the mixture to bind the vegetable fiber with the copolymer.
The molding step preferably comprises softening or melting the copolymer by heating. The heating is preferably conducted by irradiation of an electromagnetic wave.
The present invention also provides a method of recovering at least one of the vegetable fiber, saccharide, and aliphatic dicarboxylic acid from the cushioning molded product by treating the cushioning molded product with at least one of an acid, an alkali, high-temperature high-pressure water, and an enzyme.
The present invention also provides a cushioning molded product comprising a vegetable fiber as a main constituent, and a copolymer of a saccharide and an aliphatic dicarboxylic acid as a binder, wherein at least one of the vegetable fiber, the saccharide, the aliphatic dicarboxylic acid is a product recovered by the aforementioned recovery method.
The present invention further provides a package packed by use of the cushioning molded product, a wrapped matter wrapped by use of the cushioning molded product, and a sound absorption material and building material employing the cushioning molded product.
The inventors of the present invention disclosed a compatible complex composed of a polyester containing a saccharide in the main chain and cellulose (Japanese Patent Application Laid-Open No. 2000-313702), and a biodegradable adhesive employing a polyester containing a saccharide in the main chain (Japanese Patent Application Laid-Open No. 2000-328028). The above techniques utilize complex formation due to hydrogen bonding of the hydroxyl groups of the saccharide. After comprehensive investigation for more effective utilization of the above techniques, the inventors of the present invention found that
(1) a molded product of various fibers such as cellulose bound with the polyester containing a saccharide in the main chain has excellent properties of absorbing drop impact and sound, and is suitable for use as a cushioning material, and
(2) since the polyester containing a saccharide in the main chain is soluble in a nonaqueous solvent, a mixture of a vegetable fiber and the polyester enables heating and drying in a short time, and can readily be molded into a relatively voluminous and thick cushioning material relative to its surface area.
Thereby, the present invention has been accomplished.
The present invention provides a cushioning molded product produced by molding a vegetable fiber as a component by use of a copolymer of a saccharide and an aliphatic dicarboxylic acid as a binder.
The present invention is described below in detail.
(Vegetable Fiber)
The useful vegetable fiber material includes paper, cotton, straw, wood meal, strained lees, and pulp. From the standpoint of environment protection, it is very advantageous to use waste resources resulting from industrial production: waste resources such as used paper, textile material waste, saw dust, strained lees such as bagasse.
(Saccharide Copolymer)
The binder employed in the present invention is a thermoplastic copolymer containing a saccharide in the main chain. The thermoplasticity is effective for promotion of binding in a pressing operation, and for facilitation of the secondary process after the molding process as well as foaming extrusion molding.
A first advantage of the use of the saccharide in the binder is sufficient adhesiveness as the binder owing to the affinity between the saccharides including hydrogen bonding, because the vegetable fiber is constituted of a polysaccharide such as cellulose, and xylan. Similar effects are expected to be achieved by a polyolefin or a like polymer having saccharide as a side chain. However, the ones having the saccharide in the main chain can be synthesized much more simply.
A second advantage thereof is ease of production of the source saccharide by depolymerization of the polysaccharide constituting the vegetable fiber used as the main component of the cushioning molded product. Fiber waste eliminated owing to excessive fineness and insufficient strength after the fiber opening operation, or used paper having a larger content of a foreign matter can be effectively utilized as the binder-constituting component without discarding them.
The saccharide includes monosaccharides and oligosaccharides of not larger than hexasaccharide. More specifically, the monosaccharide includes glucose, mannose, xylose, arabinonse, galactose, and glucosamine. The oligosaccharide includes cellobiose, maltose, lactose, isomaltose, nigerose, trehalose, melibiose, chitobiose, cellotriose, cellotetraose, cellopentaose, cellohexaose, maltotriose, maltotetraose, maltopentaose, and maltohexaose. The oligosaccharide is not limited to those constituted of a single monosaccharide, but may be the one constituted of plural kinds of monosaccharides. The monosaccharides and the oligosaccharides may be partially substituted by a substituent such as an acetyl group. However, in view of the adhesiveness, at least a part of the hydroxyl groups are preferably kept unsubstituted. The substitution degree is not more than that in which two groups are substituted per one monosaccharide unit. A small amount of a polysaccharide may be contained as a subsidiary component.
A method for producing the monosaccharide or the oligosaccharide from the polysaccharide constituting the vegetable fiber is hydrolysis scission of the glycoside linkage of the polysaccharide by an acid such as sulfuric acid and hydrochloric acid, or an enzyme.
An aliphatic dicarboxylic acid is used as a component to be copolymerized with the saccharide. To obtain a thermoplastic copolymer, the alkylene chain has 4 or more carbon atoms for the monosaccharide, and 6 or more carbon atoms for the oligosaccharide excluding the carbons of the functional groups (Japanese Patent Application Laid-Open No. 2000-297205). The longer alkylene chain will give higher hydrophobicity and can render difficult the mixing with the fiber. Therefore, in the present invention, the carbon number of the alkylene chain is limited to be not more than 10. Specifically the aliphatic dicarboxylic acid includes adipic acid, pimelic acid, suberic acid, and sebacic acid; and acid chlorides, acid salts, and short chain alkyl esters of the above dicarboxylic acids. The aliphatic dicarboxylic acid is condensed with the saccharide in a molten state or solution state in the presence of a suitable catalyst, if necessary.
The copolymer as the binder preferably contains a component with a weight-average molecular weight ranging from 500 to 10000 unremoved for obtaining suitable hygroscopicity for effective binding in the present invention. In view of the binding strength, a component of a higher molecular weight is preferably contained simultaneously. On the other hand, a component of a molecular weight of lower than 500 is preferably excluded since the lower molecular component is liable to make instable the physical properties of the molded product.
The aforementioned copolymer component having a weight-average molecular weight ranging from 500 to 10000 is preferably contained in the copolymer at a content ranging from 50 to 100 wt %.
The vegetable fiber is contained in the cushioning molded product at a content ranging from 50 to 99 wt %, preferably from 50 to 85 wt %, and the copolymer is contained at a content ranging from 1 to 50 wt %, preferably from 15 to 50 wt %.
(Process for Production)
The vegetable fiber is subjected to fiber opening as necessary, and is mixed with a saccharide copolymer as the binder. The mixture is heated or air-dried in a suitable molding vessel to cause binding with the binder for forming a molded product. The mixing can be conducted by use of water as a solvent as in the conventional method, or by use of an organic solvent singly or in combination with water. For shorter drying time, the content of water in the solvent is preferably in the range from 0 to 50 wt %. The organic solvent includes methanol, ethanol, ethyl acetate, acetone, and dimethylformamide.
The aforementioned mixture is formed into a molded product by heating for drying and conducting binding of the binder due to softening or melting. The heating temperature is selected to be higher than the softening temperature but lower than the decomposition temperature of the binder. The heating may be conducted in the molding vessel by a conventional heater or the like, but can also be conducted effectively by irradiation with an electromagnetic wave permeable into the molded product. The electromagnetic wave includes microwaves and far-infrared rays.
The mixing ratio of the vegetable fiber and the binder is determined depending on the intended performance. A relatively less amount of the binder is liable to cause tearing of the molded product or peeling of the fiber, but will give sufficient flexibility and satisfactory hand feeling. On the other hand, a relatively large amount of the binder will give rigidity of the molded product, and will facilitate foaming extrusion molding and extrusion molding. An additive such as a plasticizer, a thickener, an antioxidant, and a colorant may be added thereto.
For mixing the vegetable fiber with the binder, in the present invention, water is not used, or the ratio of the water in the solvent is decreased in order to significantly shorten the time of heating and drying. The mixing may be conducted during or after the fiber opening with a suitable stirring apparatus. However, the method described below is more effective.
(Promotion of Powder Adhesion)
In dry mixing of the vegetable fiber and the powdery binder, the powdery binder tends to be sieved out from the fiber owing to the size difference. A countermeasure therefor is to suitably wet the fiber to promote the adhesion of the powdery binder onto the fiber.
In this method, a small amount of a liquid is impregnated into the vegetable fiber by spraying or a like method. While the fiber is wet, the powdery binder is sprinkled on the fiber and the fiber is stirred. The aforementioned liquid includes organic solvents such as methanol, ethanol, and dimethylformamide. Water is also useful. However, for shortening the drying time, the content of the water in the liquid ranges preferably from 0 to 50 wt %.
(Spraying of Solution)
In another mixing method, the binder is dissolved or suspended in an organic solvent having a relatively low boiling point, the solution or liquid suspension is sprayed onto the vegetable fiber, and the fiber is dried in situ to deposit the binder on the surface of the fiber. Since excessive penetration of the solution into the fiber may lower the binding efficiency, the spray method and the solvent are selected to avoid the excessive penetration. The solvent includes methanol, ethanol, ethyl acetate, acetone, and tetrahydrofuran.
(Fixation of Binder on Surface)
In the aforementioned production methods, the binder is dispersed in the whole vegetable fiber. However, the copolymer as the binder may be locally added on or near the surface of a pelletized fiber or of a molded fiber.
As described above, a first production process comprises a mixing or adhering step in which small particles like pellets are prepared by a mechanical method, and a binder is allowed to adhere to the surface of the particles; and a molding step in which the particles are filled into a mold and heated therein to melt the binder to bind the pelletized fiber.
In a second production process, the fiber is mechanically formed into an intended shape followed by a mixing step in which the binder is applied onto the surface of the shaped fiber, and the resulting mixture is heated for binding to fix the shape. This method is applicable to entangleable fibers for decreasing the amount of the binder.
The shape of the molded product produced by the aforementioned process can be designed for the use as the cushioning material. As the cushioning article for packing electrical appliances and precision machine products, the fiber-binder mixture is molded in a shape to fit to the profile of the products to be packed. For arranging fruits, eggs, or the like, the fiber-binder mixture is molded in a shape having protrusions and hollows corresponding to the shape of the things to be packed. In other uses, the fiber-binder mixture is molded into pellets or granules to fill the interspace between the packed content and the outer case. Otherwise, the mixture is molded in a sheet for use as a cushioning-wrapping sheet.
Generally, cushioning molded products have sound absorption properties, and are used as sound absorbing materials and building materials. The cushioning molded products of the present invention are also useful for such uses.
(Recyclability)
The cushioning molded product of the present invention can be recycled by a mechanical method in which the product is grinded, heated and remolded, or is subjected to fiber-opening in a solvent and remolded. Moreover, the source materials can be recovered. That is, in the cushioning molded product of the present invention, the copolymer contained as the binder is hydrolyzed and can be depolymerized by an acid, an alkali, high-temperature high-pressure water, or an enzyme. Therefore, under such a condition that the vegetable fiber is hydrolyzed, the saccharide and the aliphatic dicarboxylic acid can be recovered, whereas under such a condition that the vegetable fiber is not hydrolyzed, the vegetable fiber, the saccharide and the aliphatic dicarboxylic acid can be respectively recovered entirely. Through such a recovery process, the source materials can be recycled without deterioration of the quality. In other words, any or all of the vegetable fiber, the saccharide, and the aliphatic dicarboxylic acid can be used again as the source materials for production of the cushioning molded product of the present invention by the production process described above.
The cushioning molded product of the present invention, which is biodegradable owing to the above-mentioned hydrolyzability, will not cause any adverse influence even when it is thrown out into the natural environment.